Immunity in intestinal helminth infections: present concepts, future directions

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Abstract
Although intestinal helminth and protozoan infections are prevalent throughout the world, their impact is poorly known. Nevertheless, the morbidity and mortality that occur have stimulated research into host resistance and pathogenesis. Unfortunately, despite an increasing knowledge base, the actual effector molecules which lead to parasite loss are unknown. IgA antibody, intraepithelial leukocytes and mucosal mast cells are thought to be involved. The role of these and other responses in making the intestinal microenvironment hostile to the parasite through effects of neurotransmission, epithelial cell differentiation and function, smooth muscle activities, and local inflammatory responses must be studied. Future research will include: further definition of the cellular and molecular immunologic repertoire of the intestine, identification of local effector molecules and investigation of interactions between antigen-specific immune responses and intestinal physiology. Studies of human infections will be more restricted but must include: assessment of parasite-specific local immunologic responses, inflammatory events in the intestine, and development of relatively non-invasive techniques to study gastrointestinal physiology during parasitic infection. Perhaps most importantly, research facilities must be established in developing countries to investigate intestinal immunological, inflammatory and physiological responses during infection. Through such investigations, risk factors for susceptibility and disease severity may be identified and therapeutic or prophylactic strategies developed.